From FEDweek:
As was widely expected, an issue has arisen regarding repayment of Social Security taxes that were not withheld from many federal employees late last year under a Trump administration policy.
Under that policy, the standard 6.2 percent Social Security withholding was not taken from the pay of federal employees who earned less than $4,000 in a biweekly pay period starting last September through year’s end. Employees were not allowed to opt out—many said they wished to—although the Postal Service was free to decline to participate, and did, because of its semi-independent status.
From the outset, concerns arose about the requirement that the amount not withheld over those four months must be repaid (the original deadline of April 30 was extended to year-end 2021). However, because that repayment generally is made through regular payroll withholding, there have been questions about employees who separate before the amount is repaid or who work on an irregular schedule.
According to the NFFE union, those concerns proved justified when the Agriculture Department’s National Finance Center, which administers payroll there and for some other agencies, “issued notices to over 10,000 individuals demanding payment by May 2 or they would incur penalties with interest and be referred to collections.” ...